How best to render a 3D grid?
Another way to create a 3d grid could be to use a simple basic cube:


add a wireframe modifier for the cube
add an array modifier on X, fixed count (eg) 5
add an array modifier on Y, fixed count (eg) 5
add an array modifier on Z, fixed count (eg) 5


Like this:



At least you can play easily with modifiers until satisfied...

edit:

I'll try to explain (as I got it) what Mentalist suggested in comments: you can avoid the wireframe modifier, using a "wire" material, which allows to save a lot of geometry at the expenses of... geometry, ie: material wireframe width is not adjustable but also in this way you save so many vertices. 

I'll also add the option to use a different base shape (a "3d cross" instead of a cube) to save quite more (unneeded) vertices, because using cube and arrays, all cubes share all their vertices... with the "3d cross" this is slightly better.